1. Field of the Invention
The process of this invention resides in the area of removing fine particles from larger uniform size particles in a powder and more particularly relates to a process of placing the powder in a liquid, suspending the fine particles and then decanting the suspension to remove the fine suspended particles from the powder.
2. Description of the Prior Art
In many instances it is important to have a powder containing particles of like size, and it is often necessary to remove finer particles from those particles of uniform size in such particulate material. Sieving is a common procedure to try to accomplish this result. Sieving easily removes particles larger than the sieve openings, but in many cases sieving does not totally eliminate finer particles from those of the desired uniform size because the sieving process itself can result in the formation of additional fine particles especially when the particles are of a brittle nature and rub against the screen of the sieve and against one another.
In the performance of various chemical tests, uniform particle size can be crucial for accurate results. For example, in testing the iron-binding capacity of blood serum, one can perform an iron-binding capacity test to determine the total ability of the blood serum to combine with ferric ions. The iron-binding protein in serum is known as transferrin and normally is only partially bound with iron. Testing is done to measure the total amount of iron to which the transferrin is capable of binding. A sample of a patient's serum is mixed with a solution containing excess ferric ions which ions bind to the unoccupied sites on the transferrin and this mixture is brought into contact with a material which removes any unbound ferric ions. This material may be magnesium carbonate, but it has been found that this material is inconvenient to use. A more desirable procedure is to pass the mixture through an alumina column to remove such unbound ferric ions. Any remaining bound ferric iron in the serum is determined by further testing which result represents the total iron-binding capacity of the serum when the value is calculated with corrections made for the dilution of the serum by the iron solution. The actual structure for such filtering is a column containing an alumina section in it with a receipt cup below. The serum and ferric ion mixture is placed in the column and passed through the alumina into the cup for further testing. Alumina, also known as aluminum oxide, must be of a particle size that is uniform for the test to be accurate. Usually the aluminum oxide powder used in this test, even if previously sieved, contains undesired fine particles. It is these remaining fine particles that must be removed to have an alumina product of uniform particle size for highly accurate test results. It should be noted that although an example is given above for testing the iron-saturating ability of serum and its total iron-binding capacity, the process for removing fine particles of this invention can be utilized in a variety of other types of processes for producing a powder material of uniform particle size. The problem with sieving, as mentioned in the example above, is that the aluminum oxide particles can rub against the screen of the sieve and against each other, such as during shipping, causing the particles to break apart, since they are brittle, into smaller particles. Even when purchasing bulk amounts of pre-sized particles which are available as sieved factions, that is material which will pass through one size of sieve but not through another smaller size, one does not avoid the problem. One still encounters the undesired finer particles.
In the prior art this removal is accomplished by suspending the powder in a liquid such as water and letting the powder partially settle. One then discards the finer, lighter particles floating in the liquid by decantation as many smaller particles remain suspended for a period of time in the liquid. This process is very tedious and must be repeated many times to produce a satisfactory powder of uniform particle size. This lengthy process increases the cost of producing a powder of desired quality.